1. Field of the Invention
The present disclosure relates to a method for preparing a ceramic waste form containing radioactive rare-earth and transuranic oxide, and the ceramic waste form with enhanced density, heat-stability, and leach resistance prepared by the same.
2. Description of the Related Art
Pyro-processing is a technology by which effective ingredients such as uranium contained in spent nuclear fuel from nuclear power plants may be recovered and recycled for fuel in fast reactors, which are the next generation nuclear reactors, in order to significantly improve uranium utilization and greatly reduce the amount, toxicity, and reduce the amount, toxicity and calorific power of high level radioactive wastes. Pyro-processing is a core technology which constitutes the backbone of future nuclear power systems, in order to largely improve the stability and economy of nuclear power generation. Unlike conventional reprocessing technology which separates only plutonium from spent nuclear fuel, pyro-processing is acknowledged as the spent nuclear fuel utilization technology for the 21st century, which does not involve the risk of nuclear proliferation because plutonium and tansuranic elements (elements heavier than uranium in atomic weight) such as neptunium, americium, curium, etc. contained in spent nuclear fuel may be extracted together through pyroprocessing.
Pyro-processing is a dry process which uses a molten salt medium and recovers or separates useful materials through electrochemical methods such as electrolytic reduction, electrolytic refining, electrowinning, etc., and has many advantages such as device compactness and increased efficiency due to high temperature reactions. The amount of waste generated may be greatly reduced by removing radioactive rare earth elements present in waste molten salt, recycling them into recyclable molten salt, and recirculating the recyclable molten salt for reuse (Y. J. Cho, J. Nucl. Sci. Technol. (2006) 43, 1280, 1286). The technology relates to a method for preparing Nd2O3, CeO2, La2O3, and Y2O3, which are the main ingredients in an end waste product of powder rare earth oxide radioactive waste, into a stable waste form appropriate for final disposal. The preparation of a stable waste form refers to a process which uses a solidification medium to prepare powder rare earth oxide radioactive waste into a stable waste form aggregate, and the solidification medium used must contain a quantity of physically/chemically stable powder radioactive waste. Korean Patent Publication No. 1998-024918 describes a method for treating radioactive solid waste containing aluminum by using a waste form with excellent mechanical strength and characteristics, which prevents nuclides from releasing by reacting radioactive solid waste containing metal aluminum with alkaline solution, generating hydrogen gas, and adding a solidification material containing a potential hydraulic material as a main reactant ingredient. Korean Patent No. 757200 relates to a method for preparing immobilization product of waste chloride salts using zeolite only, and more particularly to a method for preparing immobilization product of waste chloride salts using zeolite only, including: mixing an alkali or alkaline earth metal such as Cesium (Cs), Strontium (Sr), Barium (Ba), etc., or a rare earth-based radioactive nuclide with zeolite to prepare an immobilization intermediate; and converting the immobilization intermediate into an Na-sodalite.
Although there are various methods in conventional technology for preparing radioactive waste into a waste form according to subjects to be solidified, there are no research results on preparation of waste consisting only of radioactive rare earth and transuranic oxide into a waste form. A waste form is prepared by a vitrification method commercially applied for treatment of high-level waste, including melting/decomposing borosilicate glass medium with a waste to be solidified (slurry generated during the wet process) at about 1400-1500° C. in an induction furnace, pouring the melt into a solidification drum, and subjecting it to a heat treatment in order to prevent cracking. Due to problems such as control of internal compositions for high frequency induction, maintenance, replacement of internal structural materials according to corrosion, complicated elements, and collection of highly volatile nuclides due to high temperatures, there are many difficulties in maintenance and much waste production. Because rare earth oxide in glass melt has a high tendency to make glass components crystalline and is precipitated to the bottom of the melt, it is difficult to prepare a homogeneous glass waste form.
Thus, the present inventors have performed studies on methods for preparing waste form containing radioactive rare earth oxide, used a ceramic solidification medium including CaHPO4 which converts rare-earth oxide into a stable monazite mineral, Zn2TiO4 which has excellent radioactive resistance, and SiO2, B2O3 or H3BO3 which serves as lowering the sintering temperature and improve the properties of the waste form, developed a method for preparing ceramic waste form containing radioactive rare earth and transuranic oxide which may be prepared from sintering at temperatures of 1000° C. or less, and completed the present invention.